Threading beads for stronger polymer gels

A team of Japanese researchers has found a new way to strengthen polymer gels by changing the length of the polymer ‘thread’ between each molecular ‘bead’. The researchers report their work in a paper in ChemComm.

A polymer gel consists of a three-dimensional cross-linked polymer network swollen with liquid molecules. However, most conventional polymer gels are brittle as a result of stress building up in their cross-linked polymer network structure. In order for polymer gels to be employed as molecular sieves and superabsorbent materials, their mechanical properties need to be improved.

Researchers from Nagoya University and The University of Tokyo have now found a way to increase the fracture resistance of polymer gels using a design based on molecular ‘beads’ and polymer ‘threads’. The molecular beads are modified cyclodextrin rings, which are threaded onto polyethylene glycol (PEG) threads. The cyclodextrin rings contain groups that allow the threaded structures to be cross-linked to form a three-dimensional polymer network that can be used as a polymer gel.

“We investigated the effect of the molecular weight of PEG per cyclodextrin ring on the strain and rupture strength of the resulting gels,” explains study co-author Yukikazu Takeoka from Nagoya University.

The researchers found that these polymer gels are resistant to fracture, due to the cyclodextrin beads being able to slide along the PEG threads when a force is applied, preventing stress from building up. The magnitude of this effect increases with the molecular weight of PEG per cyclodextrin ring, resulting in gels with greater strain and rupture strength. In other words, the ability of the cyclodextrin beads to slide along the polymer threads increases with the length of the thread between the beads.

“The ability to improve the fracture resistance of polymer gels by increasing the molecular weight of polymer units for each cross-linking cyclodextrin ring is a convenient solution to overcome the problem of the brittleness of conventional polymer gels,” says lead author Kana Ohmori, also from Nagoya University.

This approach to improving strain and rupture strength by using mobile cross-linking molecular beads threaded on polymer chains should allow the creation of polymer gels with desired mechanical properties.

This story is adapted from material from Nagoya University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.